Revert "Merge pull request #8875 from gaye/bug-830180"

This reverts commit f8621db86ae6380bca20f980a4c32403c1a18638, reversing
changes made to 10627f87346ffce9cff80e51753d35b26f15763b.
Merge pull request #9464 from gaye/bug-864398

Revert "Merge pull request #8875 from gaye/bug-830180"
Bug 865091 - Enable systemXhr so youtube bypasses CORS. r=daleharvey
Bug 845173 - [MMS][Utility] smil document generate and attchment extract utility for MMS message - r=julienw

Implements a parser and generator for SMIL XML format, the format used by gecko for MMS, which is converted to/from arrays for consuming in the sms application.

Co-Authored by @steveck-chung and @gnarf37